U.S. Pat. No. 4,001,502 (Attorney's docket PHA 20,709) discloses a straylight or flare compensation circuit which corrects for excessive dark current and which features a blanking circuit to enable a stable black level without spikes and blanking noise. Flare arises from unwanted and spurious reflections from a field illuminated by incident light and spurious diffractions and minute inclusions causing reflection phenomena in fields illuminated by transmitted light. In addition, internal reflections can occur between the surfaces of the lenses forming the optical system of the imaging device and this can contribute to the overall flare in the final image produced on the target or sensing surface thereof. Due to the unwanted reflection or transmission, an opaque portion of a field illuminated by incident light, will not appear perfectly black in the final image but instead, will appear grey. It is assumed that flare is substantially evenly distributed over the entire field and therefore that all regions will appear lighter grey than they should. The video is integrated to provide a measure of the average picture level and is added to a reference level to compare with the blanking level in the original signal. The blanking circuit has a differential amplifier with diodes to ensure a correct and stable black level without noise or spikes.
These known methods work satisfactorily so long as the average picture value is a measure for the amount of light falling on the image sensor.
The above citations are hereby incorporated in whole by reference.